The Calcium Conundrum: What It Takes To Build Strong Bones

What foods are the best sources of those bone-building nutrients? If you said milk, you're in the majority--every day we hear that milk and other dairy products build strong bones. But if you said milk, you're wrong--or at best only partly right.

Pop quiz: Name three nutrients that are critical to building strong bones. Calcium, right? Everybody gets that one. Any others? Some people get vitamin D, and they’re correct. But almost no one can come up with a third. Give up? In addition to calcium and vitamin D, healthy bones need magnesium, phosphorus, manganese, and vitamin K.

Okay pop quiz, part 2: What foods are the best sources of those bone-building nutrients? If you said milk, you’re in the majority—every day we hear that milk and other dairy products build strong bones. But if you said milk, you’re wrong—or at best only partly right. Yes, milk, cheese, and yogurt are good sources of calcium, and they do pretty well on vitamin D—if they’re “fortified,” meaning that it’s added to the milk. But they’re not even close to being good sources of most of the other important nutrients.

Let’s take a closer look at calcium, vitamin D, and some of those often-overlooked bone-building nutrients, including how much you need and where you get it.

CALCIUM is the most abundant mineral in the body, making up about two percent of our body weight. Almost all of it lives in our bones and teeth. In the U.S., the Recommended Daily Allowance (RDA) for adults is 1,000 – 1,200 milligrams of calcium per day. Calcium helps bones grow when we’re young, and keeps them strong as we age.

Milk and dairy products are excellent sources, but there are plenty of other high-calcium foods that may be even better because calcium in vegetables may be absorbed by our bodies more efficiently than animal-based calcium. Sources include kale, tofu, turnip greens, broccoli, beans, black molasses, fortified drinks (orange juice, soy milk, almond milk, rice milk), fortified cereals, salmon, and sardines.

VITAMIN D helps the body get calcium out of your food and into your bones, where it belongs. RDA is 600 – 800 IU (International Units) per day, but a lot of Americans are vitamin D deficient, which means not enough calcium gets to the bones. The result is an increase in the risk of bone fractures.

Vitamin D deficiency has been linked with a number of other health problems, including increased cancer and diabetes risk. Many experts now recommend 1,000 – 2,000 IU per day. Sunlight is by far the best source–just 10 minutes in the sun can give you up to 10,000 IU. But thanks to our current obsession with sunscreen (which is a good thing, but we still need to spend some unscreened time outside), we don’t get enough. Sources other than dairy include cod liver oil, salmon, mackerel, sole, cod, tuna, sardines, and eggs.

MAGNESIUM makes bones stronger and teeth harder. The RDA is 200-420 milligrams per day, but Americans are even more deficient in magnesium than we are in vitamin D. Many experts now recommend that we get a 1:1 ratio of calcium to magnesium (in other words if you get 500 mg of calcium, you need 500 mg of magnesium too). Excellent sources are pumpkin seeds, chia seeds, whole grains, barley, soybeans, almonds, cashews, other nuts, beets, and collard greens.

PHOSPHORUS works with calcium to build bone mass and strength. As with vitamin D and magnesium, if we don’t get enough phosphorus, our body starts jettisoning calcium, usually via urine or by creating kidney stones. RDA is about 700 mg per day. Excellent sources include soy, whole grains, barley, dairy, nuts, cheese, soybeans, sunflower seeds, and lentils.

POTASSIUM neutralizes naturally occurring acids that can eat away at our bones. RDA is 4700 mg per day (four times more than calcium), and great sources are sweet potatoes, other potatoes, cantaloupe, bananas, avocados, tomato products, spinach, beans, yogurt, halibut, mackerel, peaches, and apples.

VITAMIN K keeps calcium in the bones and out of the bloodstream. RDA is 90 micrograms (for females) to 120 mcg (for males) per day. There’s barely any vitamin K in dairy products, but a cup of kale will give you 630 mcg. Other sources include spinach, turnip greens, and other dark leafy veggies, asparagus, cabbage, and broccoli.

As you can see, strong bones are made of quite a bit more than calcium and vitamin D. Problems start when the ratio of calcium to the other nutrients gets out of whack (and it almost always is). Too much calcium may increase our risk of developing kidney stones and arthritis, and may actually lead to an increase in the risk of developing osteoporosis and suffering bone fractures. (About a third of women–and a fifth of men–over 50 will have an osteoporosis-related fracture.) And the biggest culprit is milk. Wait, what? Yep, as counterintuitive as that sounds, it’s true.

A number of international studies have found that countries where milk consumption is highest (the U.S. is at the top of that list) have the highest rates of hip and other bone fractures (we’re at the top of that list too).

What’s wrong with milk?

While milk products are high in calcium, they don’t contain enough of the other co-operating nutrients to get that calcium to the right place. Milk also contains a lot of protein, which sounds like a good thing but has its own problems. Eating a lot of animal (but not vegetable) protein–which Americans do too much of–increases bone fracture rates even further.

Oh, and it gets worse. In the China study, men with the highest calcium intake had double the risk of developing prostate cancer and four times the risk of having metastatic (mean it spread to other parts of the body) and fatal prostate cancer.

As long as we’re talking about important foods, let’s not forget about some that can have a negative effect on bone strength: these include salt, caffeine, sugar, and animal products. In moderation, they’re fine, of course. But eaten the way we typically eat them is a problem.

Finally, as important as diet is in building strong bones, it’s also important to do some weight-bearing exercise. Those include simple things like walking and jogging (but not swimming or horseback riding). Try to get 30 minutes at least five days per week.

Before you start any exercise routine or make big changes to your diet, talk with your healthcare provider about what’s best for you and your unique circumstances.